The invention concerns weighing apparatus of the type having strain guages, and it is particularly applicable to bathroom scales.
It is intended that such apparatus which, while being of a simple design, structure and low-cost is nevertheless reliable and precise.
For this purpose, the apparatus of the invention comprises a single bar integrated at its ends with a load receiving plate and with a support base respectively; at least two assemblies with strain gauges fastened to the bar sensitive to bending of the bar under the effect of the load applied, those assemblies, in combination with the zone of the bar with which they work and with a circuit to process the signals emitted by the gauges having the same measurement sensitivity for the same load applied. The apparatus further comprises at least a third assembly with a strain gauge fastened to the bar sensitive to twisting of the bar under the effect of the load applied and a circuit to process the signals emitted by the three strain gauge assemblies, further including means for combining the signals so as to eliminate in the outgoing signal the component resulting from strain of the bar in torsion.
The first two bending-sensitive assemblies contain identical gauges working together with the bar in zones of the same section.
Outside of the zones of measurement of the bending movement, the bar can be of variable section and/or composition, notably, at its fastening end or in the zone receiving the torsion-sensitive assembly.
Preferably, however, the bar is of uniform section, e.g., polygonal (square, rectangular, etc.) or curved (round, elliptical, etc.) or profiled (T, U, I, H, [, L, etc.).
The bar can be solid or tubular.
According to one preferred embodiment, each assembly contains a single gauge, the gauge of each assembly sensitive to bending being parallel to the general direction of the bar and the gauge of the assembly sensitive to twisting being inclined in that direction, e.g., by 45.degree..
In practice, each of the three strain gauge assemblies is sensitive to both bending and twisting, but for different parts, so that, by elimination of the twisting component in the outgoing signal, the bending component forming that outgoing signal is essentially defined by the two bending-sensitive components and, for a small part, the by twisting-sensitive component.